Conventionally, X-ray diagnosis apparatuses are known to use an image expressing method by which blood flow information acquired by injecting a contrast media is expressed with predetermined parameter values. In the following sections, such an image expressing method will be referred to as parametric imaging. During the parametric imaging process described above, a Time-Intensity Curve (TIC) of the contrast media is calculated for each of the pixels, and various types of parameter values are further calculated by using the calculated TICs. TICs may also be called Time Density Curves (TDCs). Examples of the parameter values calculated during parametric imaging processes include: Time To Peak (TIP) indicating the time period until the TIC reaches a peak; a Peak Height (PH) indicating the height of the peak; an Area Under Curve (AUC) indicating the area of the TIC; Arrival Time (AT) indicating the period of time it takes for the contrast media to arrive; a Wash Out value indicating the time period from the peak to the time when the contrast media finishes flowing out; and Mean Transit Time (MIT).
During the parametric imaging process, parameter values corresponding to blood flow information desired by a viewer are calculated for each of the pixels, so that an image is generated and displayed by expressing each of the pixels in the image while using a color corresponding to a certain one of the calculated parameter values. Accordingly, the viewer is able to make various types of diagnoses on the basis of the blood flow information expressed by the displayed image. For example, a diagnosis is made by taking a contrast enhanced image of both of the pulmonary arteries for the purpose of checking an embolization state of the pulmonary arteries. Such a diagnosis procedure is expected to make use of parametric imaging. For the pulmonary arteries, it is expected that a useful diagnosis can be made by comparing the manners in which the blood vessels are visibly rendered due to the contrast media between the left lung and the right lung. In other words, when any of the blood vessels has embolization, the manners in which the blood vessels are visibly rendered due to the contrast media are different between the left lung and the right lung. It is therefore possible to make a diagnosis on the embolization state of the pulmonary arteries, by observing the difference in the manners in which the blood vessels are visibly rendered.